Older adults account for a large and increasing proportion of the patients cared for in Intensive Care Units (ICUs) and many survive the ICU with new physical or cognitive impairments. Frailty, a syndrome of age- or disease-related declines in physiologic reserve may be an important risk factor for adverse outcomes after ICU treatment. The ability to test interventions geared to improving ICU outcomes in older patients has been hampered by the lack of measurement approaches for identifying frailty in critically ill patients. A junior investigator in Critical Care Medicine, with a passion for applying geriatric principles into the ICU, has developed two complementary approaches for identifying frailty in critically ill patients. The first approach identifies frailty using clinical information that can e easily obtained from the electronic medical record. The second approach identifies frailty using an assessment tool that can be administered to patients or their surrogates. The overall goal of this pilot study is to test prospectively the validity of these two innovative frailty measures in cohort of critically ill older patients. Specific Aim 1 will evaluate the construct validity of thetwo frailty measures by comparing the clinical and demographic correlates of pre-ICU frailty. Specific Aim 2 will evaluate the predictive validity of these two frailty measures by comparing their ability to predict hospital mortality. Specific Aim 3 is exploratory and will determine the association between pre-ICU frailty and the six-month outcome of death or severe disability. The results from this study will directly inform the sample size calculation and the frailty measure to be used in larger studies testing therapeutic interventions geared towards improving patient outcomes after ICU treatment. The practical experience from this project and the protected time for further career development that this award will secure will help this junior investigator transition towards a Mentored Career Development Award and will be an important building block towards a research career focused on improving outcomes for older patients facing critical illness.